The subject matter disclosed herein relates to an image processing method and an image processing apparatus both of which extract a fat region from a tomographic image of a subject, and a program used therefore.
A threshold process of pixel values is performed on tomographic images such as a CT (Computed Tomography) image, an MRI (Magnetic Resonance Imaging) image, etc., thereby making it possible to extract each fat region. A decision as to whether a metabolic syndrome is suspected, is made with a visceral fat area as one index clinically. Since, however, full fat regions are extracted simply by performing the threshold process of the pixel values, there is a need to separate a full fat region into a visceral fat region and a subcutaneous fat region.
An operator has heretofore separated a visceral fat region and a subcutaneous fat region from each other by tracing a fat region and a region containing subcutaneous fat on a tomographic image displayed on a display screen by using a pointing device such as a mouse or the like. Since, however, this method increases the burden on the operator, a method capable of separating the visceral fat region and the subcutaneous fat region from each other simpler has been expected.
Thus, several proposals have been made up to now to meet the above expectation.
There has been proposed, for example, a method for tracing a contour or profile along the outer periphery of a body surface of a subject at a tomographic image to extract a body surface region-of-interest, extracting each muscular layer of abdominal wall by a threshold process of pixel values at the body surface region-of-interest, rolling a small circle so as to cause it to contact the outer periphery of the muscular layer of abdominal wall to trace its contour or profile line, thereby extracting a visceral region-of-interest containing visceral fat, and extracting a visceral fat region from the visceral region-of-interest (refer to Japanese Unexamined Patent Publication No. 2002-222410).
There has also been proposed, for example, a method for separating a subject portion at a tomographic image into a fat pixel region and a muscle pixel region by a threshold process of pixel values, removing a skin layer, thereafter expanding each muscle pixel in such a manner that the muscle pixel region indicative of peritoneum perfectly surrounds the fat pixel region corresponding to visceral fat, setting each fat pixel adjacent to a subject's external region and a component coupled thereto as a subcutaneous fat region, further expanding the subcutaneous fat region inside by expansion of the muscle pixel, and recognizing the fat pixel region other than the post-expansion subcutaneous fat region as visceral fat (refer to Japanese Unexamined Patent Publication No. 2003-339694).
According to the method proposed by the '410 publication, however, the size of a gap or clearance in the extracted abdominal-wall muscular layer varies depending on subjects. Therefore, there is a need to suitably adjust the diameter of a small circle in order to trace the profile or contour of each abdominal-wall muscular layer suitably. Since the small circle is rolled while being shifted little by little along the profile of the abdominal-wall muscular layer and its profile line is traced, the amount of calculation increases and time is spent in processing.
According to the method proposed by the '694 publication, each muscle pixel indicative of peritoneum is temporarily expanded and a fat portion eroded by the expansion is made up. Therefore, the subcutaneous fat region is expanded inside by its expansion, whereby there is a possibility of lacking in correctness in the boundary separation between the visceral fat and the subcutaneous fat.